Lovable — Pricing calculator (Auth + Billing)

Build a Pricing calculator.

Brief: Interactive pricing with tier sliders, real-time total, contact CTA.

Variant: Auth + Billing
Supabase Auth + Stripe Checkout + customer portal + webhooks. Users gated by plan.

Technical constraints:
- Next.js 15 App Router + Tailwind + shadcn/ui.
- Supabase for data + auth (when required).
- TypeScript everywhere.
- Mobile-responsive out of the box.
- Dark mode via next-themes.
- Accessible: semantic HTML, visible focus, keyboard navigation.

Deliver:
- Database schema with RLS policies if data-bound.
- All pages with empty states, loading states, and error states.
- A seeded demo account so I can log in and see the full app without signing up.

If you can't fit everything in one pass, ship the core flow end-to-end first, then iterate.